Amyotrophic lateral sclerosis (ALS) is a severe progressive neurodegenerative disease characterized by degeneration of motor neurons in the brain and spinal cord, resulting in neurogenic muscle wasting, paralysis, and death. Nearly 95% of ALS cases have pathology featuring phosphorylated inclusions of the TDP-43 protein in neurons and glial cells. Furthermore, mutations in the gene coding for TDP-43 have been shown to cause some cases of ALS, indicating normal TDP-43 is critical for neuronal health. Phosphorylation of TDP-43 reduces its turnover, increases its aggregation, and promotes neurotoxicity and neurodegeneration. Recent work has identified the phosphatase calcineurin as a key regulator of phosphorylated TDP-43 (pTDP) accumulation. By dephosphorylating pTDP, calcineurin reduces levels of neurotoxic pTDP and protects against disease phenotypes, including neurodegeneration. An understanding of the mechanisms controlling TDP-43 pathology in ALS is critical to the design of neuroprotective strategies. This proposal describes experiments exploring the cellular and molecular changes that promote TDP-43-targeted calcineurin phosphatase activity, with a focus on the development of therapeutic interventions for the treatment of ALS. This work will 1) elucidate mechanisms controlling calcineurin activation and pTDP clearance, 2) evaluate activation of calcineurin as a novel therapeutic strategy for the clearance of pTDP, 3), provide new information about cellular recovery following neurotoxic stress, and 4) may provide additional targets for therapeutic intervention. Completion of this work will advance understanding of the disease processes underlying ALS and provide preclinical validation of a new therapeutic approach.